So I was gonna try to upload my local fdroid repository to gitlab and then access it from the FDroid client. But the furthest I got was an error message of the kind of
“Could not open zip file index-v1.jar”
which I could only see through ADB because FDroid itself very uninformatively says “Error getting index file”.

I tried the tool repomaker and if I configure that same gitlab repository to be my storage there, then it works perfectly. Until repomaker itself crashes or whatever, because apparently this is still an unstable version.

If I use repomaker, it gives me a URL to type in the FDroid client, and it works immediately. For example
https ://repomaker.grobox.de/repos/user_“number1”/repo_“number2”/repo
But if I use this fdroid nightly command or fdroid deploy even if I configure servergitmirrors and identity_file, I can’t access this repo from the client, no matter which URL I try.
I tried
https ://github.com/“username”/“reponame”
https ://github.com/“username”/“reponame”/fdroid/repo
https ://raw.githubusercontent.com/“username”/“reponame”/master/fdroid/repo/